The present invention relates to illumination apparatuses, which are provided in image-taking apparatuses such as digital cameras, and illuminates objects.
Illumination apparatuses used in image-taking apparatus generally comprise a light source, reflector which leads a luminous flux emitted from the light source forward (object side), and an optical member, such as a Fresnel lens, which is arranged in front of the light source for obtaining a predetermined light distribution characteristic.
In such illumination apparatuses, unevenness of light distribution tends to occur because of forming errors of the reflector and optical member, and displacements between the light source, reflector and optical member. An illumination apparatus has been disclosed in which a plurality of cylindrical lens surfaces having a concave shape are formed on the entrance surface of an optical member (protector) in Japanese Patent Laid-Open Application No. 2001-337372. The cylindrical lens surface is generally extends in a direction parallel to a rod-like light-emitting tube, and diverges the flash light from the light-emitting tube to reduce the unevenness of light distribution.
The miniaturization of illumination apparatuses is required according to the miniaturization of image-taking apparatuses, and the improvement of light use efficiency (light condensing efficiency) is particularly required while reducing the height of the image-taking apparatus. An illumination apparatus has been proposed in which the improvement of light condensing efficiency and the reduction of the height of the optical system are achieved by using an optical member utilizing total reflection, such as a prism and light guide.
Moreover, recent image-taking apparatuses are designed so that the inside of the illumination apparatus (the light-emitting tube, terminals, or the like) cannot be seen from the outside.
In the illumination apparatus disclosed in Japanese Patent Laid-Open Application No. 2001-337372, since the plurality of cylindrical lens surfaces for reducing the unevenness of light distribution are formed on the entrance surface of the optical member, the inside of the illumination apparatus is hard to be seen from the outside. However, it is difficult to obtain the required light distribution characteristic and light condensing efficiency in a case where the plurality of cylindrical lens surfaces are formed on the entrance surface of the above-mentioned optical member utilizing total reflection. In other words, the structure is not adequate to the illumination apparatus in which the reduction of its height is particularly required.